Title: Einstein@Home DISCOVERY OF A PALFA MILLISECOND PULSAR IN AN ECCENTRIC BINARY ORBIT

Abstract

We report the discovery of the millisecond pulsar (MSP) PSR J1950+2414 (P = 4.3 ms) in a binary system with an eccentric (e = 0.08) 22 day orbit in Pulsar Arecibo L-band Feed Array survey observations with the Arecibo telescope. Its companion star has a median mass of 0.3 M{sub ⊙} and is most likely a white dwarf (WD). Fully recycled MSPs like this one are thought to be old neutron stars spun-up by mass transfer from a companion star. This process should circularize the orbit, as is observed for the vast majority of binary MSPs, which predominantly have orbital eccentricities e < 0.001. However, four recently discovered binary MSPs have orbits with 0. 027 < e < 0.44; PSR J1950+2414 is the fifth such system to be discovered. The upper limits for its intrinsic spin period derivative and inferred surface magnetic field strength are comparable to those of the general MSP population. The large eccentricities are incompatible with the predictions of the standard recycling scenario: something unusual happened during their evolution. Proposed scenarios are (a) initial evolution of the pulsar in a triple system which became dynamically unstable, (b) origin in an exchange encounter in an environment with highmore » stellar density, (c) rotationally delayed accretion-induced collapse of a super-Chandrasekhar WD, and (d) dynamical interaction of the binary with a circumbinary disk. We compare the properties of all five known eccentric MSPs with the predictions of these formation channels. Future measurements of the masses and proper motion might allow us to firmly exclude some of the proposed formation scenarios.« less

@article{osti_22522295,
title = {Einstein@Home DISCOVERY OF A PALFA MILLISECOND PULSAR IN AN ECCENTRIC BINARY ORBIT},
author = {Knispel, B. and Allen, B. and Lyne, A. G. and Stappers, B. W. and Freire, P. C. C. and Lazarus, P. and Aulbert, C. and Bock, O. and Eggenstein, H.-B. and Fehrmann, H. and Bogdanov, S. and Camilo, F. and Brazier, A. and Chatterjee, S. and Cordes, J. M. and Cardoso, F. and Crawford, F. and Deneva, J. S. and Ferdman, R. and Hessels, J. W. T., E-mail: benjamin.knispel@aei.mpg.de and and others},
abstractNote = {We report the discovery of the millisecond pulsar (MSP) PSR J1950+2414 (P = 4.3 ms) in a binary system with an eccentric (e = 0.08) 22 day orbit in Pulsar Arecibo L-band Feed Array survey observations with the Arecibo telescope. Its companion star has a median mass of 0.3 M{sub ⊙} and is most likely a white dwarf (WD). Fully recycled MSPs like this one are thought to be old neutron stars spun-up by mass transfer from a companion star. This process should circularize the orbit, as is observed for the vast majority of binary MSPs, which predominantly have orbital eccentricities e < 0.001. However, four recently discovered binary MSPs have orbits with 0. 027 < e < 0.44; PSR J1950+2414 is the fifth such system to be discovered. The upper limits for its intrinsic spin period derivative and inferred surface magnetic field strength are comparable to those of the general MSP population. The large eccentricities are incompatible with the predictions of the standard recycling scenario: something unusual happened during their evolution. Proposed scenarios are (a) initial evolution of the pulsar in a triple system which became dynamically unstable, (b) origin in an exchange encounter in an environment with high stellar density, (c) rotationally delayed accretion-induced collapse of a super-Chandrasekhar WD, and (d) dynamical interaction of the binary with a circumbinary disk. We compare the properties of all five known eccentric MSPs with the predictions of these formation channels. Future measurements of the masses and proper motion might allow us to firmly exclude some of the proposed formation scenarios.},
doi = {10.1088/0004-637X/806/1/140},
journal = {Astrophysical Journal},
number = 1,
volume = 806,
place = {United States},
year = 2015,
month = 6
}

We report the discovery of the 20.7 ms binary pulsar J1952+2630, made using the distributed computing project Einstein-Home in Pulsar ALFA survey observations with the Arecibo telescope. Follow-up observations with the Arecibo telescope confirm the binary nature of the system. We obtain a circular orbital solution with an orbital period of 9.4 hr, a projected orbital radius of 2.8 lt-s, and a mass function of f = 0.15 M{sub sun} by analysis of spin period measurements. No evidence of orbital eccentricity is apparent; we set a 2{sigma} upper limit e {approx}< 1.7 x 10{sup -3}. The orbital parameters suggest amore » massive white dwarf companion with a minimum mass of 0.95 M{sub sun}, assuming a pulsar mass of 1.4 M{sub sun}. Most likely, this pulsar belongs to the rare class of intermediate-mass binary pulsars. Future timing observations will aim to determine the parameters of this system further, measure relativistic effects, and elucidate the nature of the companion star.« less

The millisecond pulsar (MSP) J1903+0327 is accompanied by an ordinary G dwarf star in an unusually wide (P{sub orb} {approx_equal} 95.2 days) and eccentric (e {approx_equal} 0.44) orbit. The standard model for producing MSPs fails to explain the orbital characteristics of this extraordinary binary, and alternative binary models are unable to explain the observables. We present a triple-star model for producing MSPs in relatively wide eccentric binaries with a normal (main-sequence) stellar companion. We start from a stable triple system consisting of a low-mass X-ray binary (LMXB) with an orbital period of at least 1 day, accompanied by a Gmore » dwarf in a wide and possibly eccentric orbit. Variations in the initial conditions naturally provide a satisfactory explanation for the unexplained triple component in the eclipsing soft X-ray transient 4U 2129+47 or the cataclysmic variable EC 19314-5915. The best explanation for J1903+0327, however, results from the expansion of the orbit of the LMXB, driven by the mass transfer from the evolving donor star to its neutron star companion, which causes the triple eventually to become dynamically unstable. Using numerical computations we show that, depending on the precise system configuration at the moment the triple becomes dynamically unstable, the ejection of each of the three components is possible. If the donor star of the LMXB is ejected, a system resembling J1903+0327 will result. If the neutron star is ejected, a single MSP results. This model therefore also provides a straightforward mechanism for forming a single MSP in the Galactic disk. We conclude that the Galaxy contains some 30-300 binaries with characteristics similar to J1903+0327 and about an order of magnitude fewer single MSPs produced with the proposed triple scenario.« less

We report the discovery of PSR 2303+46, the fifth radio pulsar known to be in a gravitationally bound orbit around another star. The pulsar period (1.066 s) and the orbital eccentricity (0.658) are the largest amount the five binary systems, while the orbital period (12./sup d/34) lies near the middle of the range. Evolutionary considerations suggest strongly that the companion is another neutron star. The general relativistic precession of periastron should be observable within 1 or 2 yr and, when measured, will specify the total mass of the two stars.

The discovery of PSR 2303 + 46, the fifth radio pulsar known to be in a gravitationally bound orbit around another star, is reported. The pulsar period (1.066 s) and the orbital eccentricity (0.658) are the largest among the five binary systems, while the orbital period (12.34d) lies near the middle of the range. Evolutionary considerations suggest strongly that the companion is another neutron star. The general relativistic precession of periastron should be observable within 1 or 2 yr and, when measured, will specify the total mass of the two stars. 12 references.

We present that millisecond pulsars, old neutron stars spun up by accreting matter from a companion star, can reach high rotation rates of hundreds of revolutions per second. Until now, all such “recycled” rotation-powered pulsars have been detected by their spin-modulated radio emission. In a computing-intensive blind search of gamma-ray data from the Fermi Large Area Telescope (with partial constraints from optical data), we detected a 2.5-millisecond pulsar, PSR J1311-3430. This unambiguously explains a formerly unidentified gamma-ray source that had been a decade-long enigma, confirming previous conjectures. Lastly, the pulsar is in a circular orbit with an orbital period ofmore » only 93 minutes, the shortest of any spin-powered pulsar binary ever found.« less